Weight is less of an issue than you’d imagine for most large submarines. Indeed it has far more effect on inertia and control than it does on buoyancy. Most subs have substantial reserve buoyancy and ballast tanks and ballast weights are customised for each project, even when part of a production line.
Several projects I’ve worked on were substantially over predicted weight but functioned fine in all but the most extreme circumstances.
Also, substantial amounts of equipment are stored outside the pressure hull, so while they affect size and weight, they don’t alter the pressure hull sizing. Thrusters, sensors, o2 tanks, ballast tanks, storage, etc are all in free flood areas.